Profiler TimelineView does not allow expanding of threads to their full depth on a loaded profiler capture

Steps to reproduce:
1. Create a new project
2. Add TestSampleGenerator.cs to the project (or any script that grantees a callstack deeper than 6)
3. Add TestSampleGenerator Component to an object in the scene
4. Deep profile the scene
5. Open the CPU Profilers Timeline view
6. Check that the main thread can be expanded far enough to see the sample "Tip()"
7. Save the profile to file.
8. Load the saved profile.

Expected Result: the main thread can still be expanded to see the "Tip()" sample
Actual Result: the main thread can not be expanded to see the "Tip()" sample
Reproduced on 2018.3.0b1, 2018.3.0b4
Not reproduced on 2018.3.0a11, 2018.2.14f1